1. Field of the Invention
The present invention relates to a fixing device to be used for an electrophotographic apparatus and an electrophotographic image forming apparatus.
2. Description of the Related Art
In general, in a heating and fixing device to be used in an electrophotographic system such as a laser printer or a copying machine, a pair of heated rotating members such as rollers, a film and a roller, a belt and a roller, or belts are brought into pressure contact with each other.
In addition, a recording material holding an image of an unfixed toner is introduced into a pressure-contact portion (fixing nip) formed by the rotating members and heated to melt the toner, with the result that the image is fixed to the recording material such as paper.
A rotating member with which an unfixed toner image held on the recording material is brought into contact is referred to as heating member and is called a fixing roller, a fixing film, or a fixing belt depending on its form.
As a method of heating a heating member, there are given a method involving heating a heating member by transmitting heat generated by a heat generator to the heating member through contact therewith or without contact therewith, and a method involving causing a heating member to generate heat itself.
As the method involving transmitting heat generated by a heat generator to a heating member, there is generally used a method involving heating a heating member with radiation heat by disposing a halogen heater inside the heating member. There is also used a method involving heating a heating member only in a fixing nip portion by bringing a ceramic heater into abutment with an inner surface of the heating member and sliding the ceramic heater.
As the method involving causing a heating member to generate heat itself, there has been used a method involving disposing a conductor layer made of a metal or the like as a base layer for a heating member and generating an eddy current by induction heating, thereby causing the conductor layer to generate heat itself (see Japanese Patent Application Laid-Open No. H09-171889).
Further, there has been known a method involving providing a microwave generating unit in a fixing device and generating a microwave, thereby causing a heating member to perform self-heating (see Japanese Patent Application Laid-Open No. 2010-160222).
In general, a fixing device is required to fix a toner with smaller electric power, and hence an attempt has been made to reduce portions serving as heat resistance to enhance heat efficiency. Therefore, it is important that heating of unnecessary portions be minimized and only necessary portions be supplied with heat by heating portions closer to a recording material from the viewpoint of energy saving. Thus, a system of causing a heating member to generate heat itself is advantageous in this respect.
Further, in recent years, there has been a demand for further shortening start-up time, and a fixing device is required to rapidly raise the temperature of the surface of a heating member up to toner fixable temperature, that is, to shorten warm-up time.